The present invention relates to pressure housing for in-water pressure based systems. More particularly, this, invention relates to a novel device for (1) improving the life of the transducers and electronics of underwater systems by maintaining a humidity-free and clean environment around them by avoiding the entry of humidity, dust, or any suspended particles in the air during occasional data offloading and battery replacement in a humid and dust-laden field station; (2) improving the ease of closing and opening of the pressure housing by the use of a novel arrangement thereby avoiding the use of conventionally employed cumbersome protruding and corrosion-prone locking devices such as screws, bolts, or clamps; and (3) implementing reliable transmission of water pressure to the pressure port of the transducer, simultaneously minimizing the errors arising from dynamic pressure effects, preventing its chemical corrosion from saline water, and arresting, bio-fouling in the vicinity of the pressure inlet.
Hitherto known in-water pressure based systems [V. B. Peshwe, S. G. Diwan, A. Joseph, and E. Desa, xe2x80x9cWave and Tide Gaugexe2x80x9d, Indian Journal of Marine Sciences, Vol. 9, pp. 73-76 (1980)] describes a Wave and Tide Gauge wherein the underwater electronics and the pressure sensor are placed and secured on a circular brass plate which fits into a brass cylinder. O-rings are used for sealing the underwater unit, which is mounted on a steel base. All steel components are nickel-plated, and the brass components are coated with paint. The pressure sensitive metallic diaphragm of the pressure transducer is protected against chemical corrosion with the use of an oil-filled neoprene nipple attached to a stainless steel coupler located on the flat face of the removable end-plate and hydraulically connected to the pressure port. The end-plate is locked to the flange of the cylindrical housing with the use of four bolts, washers, and nuts that are located in diametrically opposite sense. The disadvantage of this arrangement is the occasional damage to the neoprene rubber nipple arising from fish bites, resulting in the loss of oil that protects the pressure port of the transducer against chemical corrosion. Another drawback is protrusion of bolts and nuts, which provides a poor aesthetic appearance of the housing.
An alternate system, [A. Joseph and E. S. Desa, xe2x80x9cA Microprocessor-Based Tide Measuring Systemxe2x80x9d, Journal of Physics, E. Scientific Instruments, Vol. 17, pp. 1135-1138 (1984)], describes a tide measuring system that consists of a cylindrical underwater pressure housing made of brass, containing a Paroscientific quartz pressure transducer. The said pressure transducer is located on a circular brass base-plate of the housing, with the pressure inlet exposed t seawater through an O-ring-protected orifice on the base-plate. The entire housing is sealed with another larger O-ring located between the cylindrical housing and its base-plate. The said base-plate is mounted to the circular flange of the cylindrical housing with the use of 6 units of stainless steel bolts, washers, and nuts. A drawback of this methodology of sealing the pressure housing is that special care has to be taken to tighten the diametrically opposite bolts one at a time. Failing to do so can damage the O-ring by exceeding its elastic limit, thereby resulting in the possibility of leakage of the pressure housing and the damage of the transducer. Another drawback observed was that the underwater connector used for the transfer of data to an external readout unit suffered chemical corrosion after extended submergence in seawater. The hydraulic coupling device incorporated with the Paroscientific quartz pressure transducer comprises a silicone-oil-filled flexible plastic capillary tube of internal diameter xcx9c1 mm and length xcx9c200 mm, having one end attached to the pressure port of the transducer and the other end connected to the end-cap of the transducer housing. The drawback observed with this hydraulic coupling device in field studies is a slow leakage of oil over time.
Another system, [A. Joseph and E. Desa, xe2x80x9cAn Evaluation of Free- and Fixed-Vane Flow Meters with Curved- and Flat-Bladed Savonius Rotorsxe2x80x9d, Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol.11, No.2, pp.525-533 (1994)] describe two types of current meters-cum-depth indicators that use in-water pressure housing to locate sensors and electronics printed circuit boards. In these instruments the pressure housing is closed with an end-plate assembly that formed part of the supporting mechanism for the water current sensor. The pressure sensor used for estimation of water depth is located on a horizontal step of the pressure housing. The said pressure housing is attached to the end-plate assembly with the use of four equally spaced bolts. Two disadvantages observed with this arrangement are (1) protruding locking bolts and (2) a protruding pressure inlet that is vulnerable to deterioration in pressure measurement accuracy resulting from the adverse influence of flows, waves, or a combination of flows and waves as discussed by A. Joseph, J. A. E. Desa, P. Foden, K. Taylor, J. McKeown, and E. Desa [in: xe2x80x9cEvaluation and performance enhancement of a pressure transducer under flows, waves, and a combination of flows and waves, Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 17, No. 3, pp. 357-365 (2000)].
In yet an other version of in-water pressure devices for measurements of water current, water level, and many other oceanographic parameters, Aanderaa Instruments (Norway) uses a cylindrical metallic housing having a removable end-cap at one end, and a fixed end-cap at the other end, wherein the removable end-cap is locked with the use of two metallic clamps that are hooked into slots that are carved out on the diametrically opposite positions on the periphery of the end-cap and the cylindrical housing. In these devices the pressure transducer""s pressure inlet protrudes out and, therefore, suffers from pressure-measurement errors induced by various kinds of water motion in its vicinity.
The principal drawback with all conventional underwater pressure housings that are constructed from metal and whose metallic end-caps are locked with the use of devices such as metallic screws, bolts, or clamps is that they suffer from chemical corrosion after prolonged exposure to seawater, and makes opening of the end-plates usually difficult. Further, the presence of these protruding devices reduces the aesthetic appearance of the pressure housing.
The main object of the present invention is to improve the life of the transducers and the electronics of any underwater systems by maintaining a humidity-free and clean environment around them by avoiding the entry of humidity, dust, or any suspended particles in the air during occasional data offloading and battery replacement in a humid and dust-laden field station.
Another object of the present invention is to improve the ease of closing and opening of the pressure housing by the use of a novel arrangement thereby avoiding the use of conventionally employed cumbersome protruding and corrosion-prone locking devices such as screws, bolts, or clamps.
Yet another object of the present invention is to implement reliable transmission of water pressure too the pressure port of the transducer, simultaneously minimizing the errors arising from dynamic pressure effects, preventing its chemical corrosion from saline water, and arresting bio-fouling in the vicinity of the pressure inlet.
The novel pressure housing for in-water pressure based systems of the present invention provides for:
(1) Improving the life of the transducers and the electronics of any underwater systems by maintaining a humidity-free and clean environment around them by avoiding the entry of humidity, dust, or any suspended particles in the air during occasional data offloading and battery replacement in a humid and dust-laden field-station. The system of the present invention provides for two independent compartments, a transducer-cum-electronics compartment that is exclusively meant for housing the transducers and the electronics (that are not to be disturbed) and a battery-cum-connector compartment exclusively meant for housing the battery and the computer-interfacing connector, thereby providing a means for housing the environmentally sensitive transducers and the electronics in a clean and humid-free environment by avoiding the entry of humidity, dust, or any suspended particles in the air during occasional data offloading and battery replacement performed in the remote field stations, in an often dusty and moist coastal environment. Further, the two compartments are carved out from a single solid non-metallic material for elegance, lightness, and non-corrosiveness in a marine environment.
(2) Improving the ease of closing and opening of the pressure housing by the use of a novel arrangement thereby avoiding the use of conventionally employed cumbersome protruding and corrosion-prone locking devices such as screws, bolts, or clamps. The system of the present invention provides for a threaded non-metallic locating-ring to locate the seal-plate of the transducer-cum-electronics compartment in its assigned position. The system of the present invention further provides for a threaded cylindrical portion that is carved out on the top central portion of the non-metallic seal-plate of the battery-cum-connector-compartment which functions as a simple mechanism that facilitates trouble-free opening of the said seal-plate. The said seal-plate, having a threaded central male portion, is simply pushed into position, and rests on a circular step carved out from the inner surface of the cylindrical pressure housing. A threaded non-metallic end-cap (provided with a female portion for use during opening) placed over the said seal-plate locates it in position. A threaded non-metallic locating-ring keeps the seal-plate and the end-cap in its assigned position. Further, the system of the present invention allows for easy opening of the battery-cum-connector-compartment by first unscrewing the said locating-ring, opening out the end-cap, coupling the female portion of the end-cap with the male portion of the seal plate, and then pulling it out with ease and comfort.
(3) Implementing reliable transmission of water pressure to the pressure port of the transducer, simultaneously minimizing the errors arising from dynamic pressure effects, preventing its chemical corrosion from saline water, and arresting bio-fouling in the vicinity of the pressure inlet with the use of a compact, non-corrosive, bio-fouling-resistant hydraulic coupling device. Thus, the system of the present invention provides for a hydraulic coupling device (HCD) that consists essentially of a male component and a female component. A copper cylindrical rod machined in the form of a counter-sunk screw and a second copper cylindrical rod having internal and external threading constitutes the male and the female components respectively of the HCD. This coupling device forms an integral part of the pressure transducer as well as the end-cap of the transducer-cum-electronics compartment of the pressure housing. These components, together wit the viscous oil deposited within the space between the front-end of the pressure transducer and the said counter-sunk screw, form the HCD of the system of the present invention. The narrow gap between the threads of the male and the female components of the HCD provides the requisite path for transmission of seawater pressure to the pressure-port of the transducer, via the oil medium, thereby hydraulically connecting the pressure transducer to the surrounding saline water medium. The copper material of the HCD, because of its ability to repel marine growth, as reported by J. E. Huguenin and F. J. Ansuini in [xe2x80x9cThe advantages and limitations of using copper material in marine aquaculturexe2x80x9d, Proc. IEEE Oceans ""75, pp. 444-453 (1975)], eliminates the possibility of closure of the pressure inlet by bio-fouling during its prolonged exposure to the euphotic water medium. The viscous oil present within the HCD inhibits physical contact of the pressure-sensing element with the seawater, at the same time transferring the seawater pressure to the transducer (i.e., hydraulically coupling). The HCD provided in the system of the present invention allows for easy replacement of oil by merely unscrewing its male component from its slot, pouring oil into the pressure port, and then screwing it back again, thereby preventing trapping of air bubbles or other hollow closed spaces within the oil reservoir. The HCD provided in the system of the present invention is suitable for integration to the end-cap of the pressure housing. The time-constant of the spiral-shaped oil path provides a certain level of mechanical filtering of the high-frequency oscillations present in pressure measurements, caused primarily by wind-induced gravity waves and secondly by the movements of ships and boats. Because the compact flat face of the HCD provided in the system of the present invention remains flush with the flat end-plate of the pressure housing, dynamically induced measurement inaccuracies arising from the influence of flows, waves, or a combination of flows and waves are minimized, as reported by A. Joseph, J. A. E. Desa, P. Foden, K. Taylor, J. McKeown, and E. Desa [in: Evaluation and performance enhancement of a pressure transducer under flows, waves, and a combination of flows and waves, Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 17, No. 3, pp. 357-365 (2000)]. The simpler design of the HCD incorporated in the present invention of a novel pressure housing for in-water pressure based systems allows a much easier and more economically feasible construction that heretofore been unknown. Accordingly, the hydraulic coupling device incorporated in the present invention of a novel pressure housing for in-water pressure based systems is superior to all the hitherto known hydraulic coupling devices including those described by J. H Filloux [in xe2x80x9cDeep sea tide gauge with optical readout of Bourdon tube rotationsxe2x80x9d, Nature, Vol. 226, pp. 935-937 (1970); G. Dietrich, K. Kalle, W. Kraus, and G. Siedler [in xe2x80x9cMeasurement of water level variationsxe2x80x9d, General Oceanography: An Introduction, pp. 128-131 (1980)]; and E. Desa, A. Joseph, D. Rodrigues, V. N. Chodankar, and S. Tengali [in xe2x80x9cAn improved hydraulic coupling de vice for use with in-water pressure based systemsxe2x80x9d pending Indian Patent Application No. 487/DEL/99].
Accordingly the present invention provides a pressure housing for in-water pressure based systems, which comprises a housing [12] having two compartments [13] and [14], the two compartments being separated from each other by a circular disc [15], one of the said compartments [13] dedicated to mount the transducers and the electronics and the other compartment [14] dedicated to locate the batterypack and the electric connector that would interface to a computer or any other device that enables initialization of the electronics and data offload, an electrical connector [16] provided with an O-ring [17] and axially located at the center of the circular disc [15] to electrically connect the two compartments [13] and [14], a seal plate [18] provided with a pair of lateral O-rings [19] and [20] to weatherproof the transducers-cum-electronics compartment [13], a retainer ring [24] for locking the seal plate [18] in its designated position, another seal plate [21] provided with a pair of lateral O-rings [22] and [23] to waterproof the batterypack-cum-connector compartment [14], a retainer ring [25] for positioning the seal plate [21] in its designated location, and a lock ring [26] for locking the retainer ring [25], a hydraulic coupling device consisting essentially of a female component [28] and a male component machined in the form of a counter-sunk screw [29], wherein the said female and male components form an integral part of the pressure transducer [30] as well as the end-cap [18] of the transducer-cum-electronics compartment [13] of the pressure housing [12], the said two components, together with the viscous oil deposited within the space provided between the front-end of the pressure transducer and the said counter-sunk screw, and the narrow gap between the threads of the said male and the female components of the hydraulic coupling device providing the requisite path for transmission of seawater pressure to the pressure-port of the transducer, thereby hydraulically connecting the pressure transducer to the surrounding saline water medium, a hollow cylindrical shaped transducer-retainer [31 ] screwed on the inner face of an axial recess on the seal plate [18] for providing mechanical stability to the pressure transducer [30], another hollow cylinder [32] screwed on the outer face of a step on the seal plate [18] for mounting two clamps [33] which serve as means for mounting the printed circuit board (pcb)[34], with the use of four similar screws [35], a hollow space carved out from a metal bolt [36], rendered waterproof with the use of an O-ring [37] for locating a temperature sensor [38] for measurement of water temperature, a t atterypack [39] for supplying electric power to the circuits and sensors, and a computer-interfacing means [40] for initialization and data offloading.
In one embodiment of the invention, the body of the pressure housing [12], the seal plates [18] and [21], and locking rings [24], [25], and [26] are all fabricated from non-metallic materials to prevent chemically induced corrosion during prolonged submergence in seawater or polluted water bodies.
In a further embodiment of the invention, the retainer ring [25] for positioning the seal plate [21] in its designated location, and a lock ring [26] for locking the pressure housing avoids the necessity for use of conventionally used protruding bolts, nuts, or clamps.
In yet another embodiment of the invention, the hydraulic coupling device is provided with a female component [28] and a male component [29], both being selected from copper or copper alloy, or any other alternate material capable of inhibiting bio-fouling in the vicinity of the pressure inlet.
In another embodiment of the invention, the hydraulic coupling device is provided with a flat termination that is located on the flat seal plate of the pressure housing and flush with it in such a manner as to abate dynamically induced pressure-measurement inaccuracies arising from the influence of flows, waves, or a combination of flows and waves.
In a further embodiment of the invention, the cylindrical collars [43] of the mounting device are provided with two cushioning non-metallic collars [44] sandwiched between the metallic collars and the curved surface of the two groves carved on the surface of the non-metallic pressure housing, thereby preventing possible biting action on the pressure housing by the metallic Collars.
In yet an other embodiment of the invention, a self-adhesive polyester thin film sticker is used protect the smooth surface areas of the non-metallic pressure housing against marine growth and the metallic mounting device against pitting action, thereby enhancing the health of the pressure housing and the mounting device and enabling their trouble-free cleansing after retrieval from the seawater after prolong submergence.
In another embodiment of the invention, the use of self-adhesive polyester transparent thin film stickers maintains the original colour and texture of the pressure housing and its mounting device, and provides an additional means for preserving the text stamped on the pressure housing.